As one of optical communication techniques, there is a technique for wavelength multiplexing of light having plural wavelengths (may be referred to as “channels”) with high density and transmitting the wavelength-multiplexed light.
Such an optical transmission technique may be referred to as “super-channel transmission.” In the super-channel transmission, by narrowing the spectrum of the signal light to be transmitted by using digital signal processing, a channel spacing may be more narrowed than that in conventional wavelength division multiplexing (WDM) transmission. Therefore, it is possible to improve the frequency utilization efficiency of an optical transmission band available in an optical transmission system.
Related techniques are disclosed in, for example, Japanese Laid-Open Patent Publication No. 2010-226169, Japanese Laid-Open Patent Publication No. 2012-023607, and Japanese Laid-Open Patent Publication No. 2014-014017.